Anyone would immediately understand why Erin Weaver so badly wanted the lead in “Xanadu,” a musical requiring her to sing, roller-skate, be in peak physical condition and, of course, spend lots of nights away from home:

For one thing, she doesn’t read music. For another, she hardly knew how to skate. And then there was that other minor detail: She gave birth just five months before rehearsals began.

“Ignorance is bliss,” Weaver says with a giggle, over breakfast in a diner, her eggs over easy on a plate, and daughter Maisie perched contentedly next to it on the table, in an infant seat. “Thank God I didn’t know how hard this was going to be.”

“This” is the role of Clio, a.k.a. Kira, the sexy, skating, singing star of “Xanadu,” a spoofy musical sendup of an awful Olivia Newton-John movie, and the decade it ushered in, the ’80s. Weaver plays the role of a demi-goddess come to life in a beachside mural who takes it upon herself to steady the misspent adulthood of Sonny, an empty-headed lug played by Charlie Brady, wearing a hideous tie-dyed shirt and equally hideous canary-yellow headband.

Weaver, a New Jersey-born actress who is regularly cast in productions at Round House Theatre and Folger Theatre and is married to stage director Aaron Posner, is a flat-out revelation in “Xanadu.” The show, genially cobbled together by playwright Douglas Carter Beane and giddily mounted for Signature Theatre by a director rising in local stature, Matthew Gardiner, features a dozen rock ditties from the period, such as “Evil Woman,” “Magic” and “Have You Never Been Mellow.” Kira has to sing in all but a couple of them, and much of the time on skates.

It’s not often that a performer working on Washington stages gets this kind of breakout opportunity — or projects as much magnetism as Weaver musters here. Prior to “Xanadu,” her work in straight plays was effective: She made a strong impression as the precocious Thomasina in Folger’s 2009 revival of Tom Stoppard’s “Arcadia.” But such portrayals did not prepare audiences for her coquettishly charismatic turn as Kira.

“I think she’s dazzling,” says Gardiner, who saw her in a production last year of “The Comedy of Errors” at Folger and was intrigued. (That show was directed by Posner; in the eternally interconnected ways of D.C. theater, Gardiner’s identical twin brother, James, just finished a run in Posner’s latest at Folger, “The Taming of the Shrew.”)

“I was sitting there, and I was just blown away by her ability as a comedian, and I said to Posner at intermission, ‘Does she do musicals?’ ” Gardiner recalls. “He said yes and sent me a recording of her singing.”

One gleans that in making his casting decision, Gardiner, who both directed and choreographed the show, went on faith. The petite but tomboyish Weaver, who is in her 30s but could pass for 24, auditioned for the physically demanding role when she was five months pregnant. She told Gardiner that though she wasn’t a dancer per se, she was athletic and had played soccer. How he intuited that a year later she would have the desire to master acrobatic and singing skills while still breast-feeding a baby is one of those mysteries of the theater universe.

“When we made her the offer, I said, ‘Are you sure that this is something you want to do?’ ” Gardiner says. “She said, ‘Absolutely. Once I have Maisie, I’m going to want to do something else, too.’ ”

Boy, she got her wish. “Aaron bought me roller skates and all the protective gear for Christmas,” explains Weaver, who lives with her husband and daughter in Prince George’s County. “A month before rehearsals started, I would roller-skate around the neighborhood.”

Weaver grew up in southern New Jersey in a theatrical family: Her mother and father are drama teachers. She majored in theater at Philadelphia’s University of the Arts. Upon graduating she settled into an actor’s life in the city, where she met Posner, who co-founded the Arden Theatre there. (The couple moved to the Washington area about a year ago, after Posner left a job as artistic director of Two River Theater Company in Red Bank, N.J., and began to find even more work in the District.)

As eager as she was to get back to the stage after the birth of Maisie, who’s 7 months old, the transition proved to be far more grueling than she ever anticipated. The challenge not only concerned the multiple dimensions of rehearsals — Weaver says she’s a stickler for preparing for roles months in advance — but also how she would care for Maisie. She’s worked out a regimen, she says, that, thanks to her husband and her younger sister Caitlin, who’s moved in for a spell, ensures that her daughter is always tended to. On weekends, the baby accompanies the actress to the theater, which has set up a separate nursery for them.

The process, however, of becoming a demi-goddess of the musical theater was daunting.

“I watched the movie and thought, ‘Olivia Newton-John didn’t do anything THAT fancy,’ ” she says. Then came “skate camp” with Gregory Vander Ploeg, a onetime performer in the Las Vegas company of “Starlight Express,” a long-running Andrew Lloyd Webber musical about trains and performed on roller skates, too.

“He started showing me stuff he was going to teach me,” Weaver says. “And that’s when the panic set in.”

She had never even skated backward before. “Xanadu” would be an amateurish mess if Weaver (and the other skaters in the cast) did not look at ease and proficient gliding across the stage.

“There were some good falls, we had some good laughs and a lot of sweat and a lot of aching muscles,” says Vander Ploeg, who since hanging up his skates has become a manager with a company that tours shows.

“She truly gained her confidence with her and me in the rink,” he says. “She’s very athletic, and with the nature of that athleticism she was able to pick that up.”

Just as difficult for her was the ultra-feminine dimension of Kira, an aspect of the character that she says did not come naturally to her. (“I told her, ‘You have to feel you’re Beyonce,’ ” says her director.) “I don’t own pink things,” she notes, adding that to get in touch with her frilly side, she asked Caitlin to “Go to Target, get a lot of little tennis skirts, to get me into character.”

Ultimately, the tension got to her. At a rehearsal of the finale, she flubbed a musical moment again and again. With the cast and crew watching, she momentarily fell apart. “I couldn’t pick up the cue,” she recalls. “It was something so small and there was such a long list of things I had to do. I was laughing, and then it just turned to crying.”

Gardiner took her aside and said: “This is nothing. You’ll get this.” Weaver remembers his reassuring words, and wells up at the memory. She did, of course, and when the cue was hit, the cast burst into applause.

Of such backstage catharses are musical-theater careers coaxed into being. Gardiner sounds as if he knew Weaver was right for musicals before she ever did.

Book by Douglas Carter Beane, music and lyrics by Jeff Lynne and John Farrar. Directed by Matthew Gardiner. Through July 1 at Signature Theatre, 4200 Campbell Ave., Arlington. Call 703-820-9771 or visitwww.signature-theatre.org.

Peter Marks joined the Washington Post as its chief theater critic in 2002. Prior to that he worked for nine years at the New York Times, on the culture, metropolitan and national desks, and spent about four years as its off-Broadway drama critic.

Comments our editors find particularly useful or relevant are displayed in Top Comments, as are comments by users with these badges: . Replies to those posts appear here, as well as posts by staff writers.

To pause and restart automatic updates, click "Live" or "Paused". If paused, you'll be notified of the number of additional comments that have come in.

Comments our editors find particularly useful or relevant are displayed in Top Comments, as are comments by users with these badges: . Replies to those posts appear here, as well as posts by staff writers.